This project will investigate intravenous and oral drug self-administration in baboons. Research will characterize the self-administration of two major drug classes: the benzodiazepines and the mixed opioid agonist/antagonists. A series of studies with the benzodiazepines will examine intravenous and oral benzodiazepine self-administration in a group of benzodiazepines which have different durations of action (e.g., chlordiazepoxide, oxazepam, midazolam). Another set of studies will explore the influence of environmental factors (i.e., conflict situations involving schedules of food delivery and electric shock punishment) which may interact with or contribute to the reinforcing effects of the benzodiazepines. The initial set of studies with the mixed agonist/antagonists will examine intravenous self-administration of a series of these compounds (e.g., nalorphine, pentazocine propiram, butorphanol and buprenorphine). Subsequent studies will more fully examine the reinforcing properties of buprenorphine by characterizing and libitum self-administration and by investigating the effects of chronic morphine administration on buprenorphine self-administration. Another set of studies will use a discrete-trial choice procedure to explore the influence of a series of mixed agonist/antagonists on intravenous heroin reinforcement.